1. Field of the Invention
The present invention relates to systems for washing the cuttings which are separated from water environment oil well drilling mud, and more particularly relates to a system for washing such cuttings and separating them from the mud residue, including oil, so that the cuttings may be disposed of in the surrounding water without oil pollution thereof.
2. General Background and Prior Art
In off-shore drilling, an emulsion, or "mud", is continuously pumped down the hole through the drilling joints so that the drilling cuttings may be washed away with the mud as it circulates back to the surface through the annulus surrounding the drilling line. So that the mud may be re-used, it is necessary to remove the cuttings it has picked up. Cutting separators, known in the art as "shale shakers", perform this separation function by means of a vibrating screen which "catches" the cuttings while allowing the mud to drip through where it is collected for re-use. The accumulated cuttings are then deposited in a wash trough which carries the cuttings, much as a flume carries logs, to a washer/separator some distance from the shale separators.
In the prior art washing is performed using a receiving tank, filled with washing solution. The cuttings are dropped from the trough into the tank where they are washed. The accumulated cuttings at the bottom are pumped out through an opening located at the bottom of the tank to another shale separator or shaker located immediately above the tank. The washing solution drips through the screen while the now clean cuttings are deposited into the surrounding water. Part of the pumped cuttings filled solution is diverted to the top of the wash trough to carry the cuttings deposited there down the trough as described above.
This system has several disadvantages. First these washer/separators are by design necessity, at least 10 feet tall. Since drilling rigs generally have an inter-tier spacing of only 8 feet, a separate platform section must be constructed to accomodate it. Second, the cuttings tend to collect at the opening of the pump and clog it. The cuttings also stick to the pump blades and clog the pump itself, as well as causing damage to the pump. Damage of this kind occurs regularly and the entire separation system must be shut down on a regular basis to clean the pump and tank. Third, the shale separator screens wear out regularly and must be replaced, with accompanying additional shut down time. Fourth, sea water washing solutions must be used to prevent the shale, composed usually of Montmorillonite clay, from breaking up and causing even more frequent and severe clogging of the pump system. Fifth, separator screens do not effectively remove all of the sand, some of which remains in suspension in the washing solution and causes abrasion of the pump mechanism. This results in even more frequent maintenance shut-downs.
The present invention solves all of these problems.
3. General Discussion of the Invention
The present invention includes a receiving tank for the cuttings deposited from the wash trough. The cuttings fall through an agitation subchamber which insures thorough washing of the cuttings, while keeping solution agitation confined to the subchamber. The washed cuttings fall by the action of gravity through the bottom of the subchamber to the bottom of the tank. The bottom of the tank is sloped toward the center where a trough like subextension of the tank houses a horizontally placed auger. As cuttings fill the tank, the solution level rises due to displacement. When the level has risen a predetermined amount, a level activated switch turns on a motor which drives the auger and at substantially the same time opens a drain valve at the outlet end of the auger. The auger pushes the cuttings through the valve where they may be deposited in the surrounding water. When the solution level then drops to a pre-determined level, another level activated switch closes the valve and stops the auger, again at substantially the same time.
The intake for the return wash solution which washes the cuttings down the wash trough is placed substantially above the settled cuttings and away from the agitation subchamber yet below the lowest level of the wash solution. The return wash solution thus remains highly ree of cutting debris. The advantages of the invention are as follows:
First: The device may be less than 8 feet tall, and in the preferred embodiment is, in fact, 7 feet tall, thus eliminating the need for drilling rig modification.
Second: Shut down due to pump clogging is virtually eliminated, since the return wash solution is highly free of cutting debris.
Third: Since the device does not use a "shale shaker" screen replacement and accompanying shut down is eliminated.
Fourth: Fresh water washing solution may be used because shale cutting break up does not affect the operation of the system.
Fifth: Since gravity, rather than screens, are used to cause separation, much finer filtration is effected and less abrasive sand remains in solution. Pump life is greatly extended.